A decision on whether to adopt a new engine for the Lockheed Martin F-35 is due to be made in the coming months as part of a suite of enhancements for the aircraft.

Speaking to a Potomac Officers Club gathering in Washington DC on 26 July, US Air Force Secretary Frank Kendall said he doesn’t want to drag the decision process out, and expects to make a decision in the next few months on whether to proceed with new technology engine to replace the current P&W F135 as part of the Joint Strike Fighter Block 4 upgrade.

The main options appear to be a Pratt & Whitney adaptive cycle engine, dubbed XA101, or General Electric’s own XA100 adaptive cycle engine. Both engines have received concept-development funding over the few past years as part of the USAF’s Advanced Engine Transition Program (AETP) which was originally established to develop an engine for the manned Next Generation Air Dominance (NGAD) platform.

Adaptive cycle engines provide more power with lower fuel flow due to new technology which focus on third-airstream capability, adaptive-cycle controls, and advanced materials which allow them to run cooler which aid fuel consumption and reduces the aircraft’s infra-red signature. They reportedly can also provide more electrical power which would enable directed energy weapons or advanced electronic warfare systems to be employed.

General Electric claims the adoption of the XA100 would increase the F-35A’s range by 30 per cent, reduce its fuel consumption by 25 per cent, and improve its thermal management capabilities by 100 per cent.

Kendall said he hoped to make a decision on the new engine in time for the 2024 Defense Budget. “I think we need to make some decision about the future of the F-35’s engine and get on with it,” he said. “I don’t want to limp along, spending R&D money on a program we either can’t afford or that we’re just not going to get agreement on among the different services,” he added, saying that there are potential obstacles to the AETP program progressing.

“One is the high cost. It’s going to take several billion dollars and a five-year program to move through EMD (engineering and manufacturing development) to get that program ready to be fielded.” He added that the AETP engines will also not fit the F-35B short takeoff and vertical landing (STOVL) variant of the JSF, thus removing the benefits of engine commonality with the other two variants.

Apart from the AETP engines, Pratt & Whitney reportedly has developed an F-135 Enhanced Engine Package upgrade for the existing F135 which may be a far more economical option, and was actively spruiking it at July’s Farnborough Airshow.